Industrial machines which are operated by an operator frequently require remotely located hand operated or foot operated switches for safe operation. Palm buttons are used in situations where a workpiece can be placed in a machine with the workpiece being supported by the machine. Palm buttons are preferred in such situations because both hands of an operator must be placed on and remain on the palm buttons to cause the machine to operate. This prevents the operator from being injured by foreseeably dangerous moving machine components.
However, some machines must be operated while the operator's hands remain on the workpiece. For example, power presses operating on large workpieces, press brakes, hydraulic bending machines, forging presses, power saws, slitting machines and many other types of machines often require the operator to support or manipulate the workpiece during the operating cycle the machine. These types of machines frequently utilize a remotely located foot pedal. Conventional foot pedals include a base to support a switch which may be partially covered by a shield.
Generally, OSHA regulations require comprehensive shielding of dangerous machine components such as pinch points in a power press, exposed edges of cutting tools, and rotating shafts of machines, especially when the machine is operated by a foot pedal. Production operators under pressure to manufacture production parts and skilled tradesmen operating machine tools to fabricate unusual parts may be tempted to remove mandatory safety guarding if and when provided by the manufacturer or employer, to make the workpiece more accessible. When the machine guards are removed, or applicable interlocks by-passed, machine operators are exposed to hazardous conditions.
For example, production power press operators can very easily be injured if their hands are caught in the power press. Such injuries will foreseeably result in crushing or amputation of an operator's fingers, hands, or arms or other body parts. Operators of power turning tools such as roll-benders or other rotating machines may be injured if their hands or clothing become caught in the machine. Many unfortunate yet foreseeable injuries resulting from these types of industrial machines present a major problem for manufacturing companies and their employees. Every effort should be made by machine designers, fabricators, manufacturers, distributors, and users to prevent the carnage of industrial workplace accidents which cause incalculable losses of life and limb and cause unnecessary personal suffering.
Foreseeable to the industry at large, including machine manufacturers and foot pedal manufacturers is that some production jobs require workers to perform repetitive tasks hundreds of times per hour to meet quotas. There is considerable pressure on such production operators to increase their speed to boost their output resulting in an incentive to remove guarding on machines and operate them in an unsafe repetitive mode. Repetitive operation of a machine equipped with a foot pedal results in what is commonly referred to as "riding the pedal." An operator may develop a rhythm which corresponds to the machine cycle time and rock back and forth on the pedal to maximize productivity. Industrial accidents may occur when an operator rides the pedal and moves his hands into the machine during its operating cycle.
Additionally machine operators, while performing their repetitive tasks, will foreseeably be subjected to job and human related stresses and diversions that will affect their ability to perform these repetitive tasks in a safe and consistent manner. Distractions could include a co-worker or supervisor calling the operator's name or a loud noise in the plant. Stresses include fatigue, pain, discomfort, problems at home, etc.
For example, an operator may improperly locate a workpiece in a machine and reach into the machine to reset it while his foot is still near the pedal. Any inadvertent foot motion would then operate the machine causing injury to the operator. This foreseeable industrial safety hazard could be prevented if the operator is required to remove his foot from the foot pedal entirely for each cycling of the machine.
Many foot pedal switches of the prior art do not completely enclose the switch utilized to operate the machine. Thus, it is foreseeable that the machine can be inadvertently triggered by foreign objects such as bars or beams or wires which contact the switch. In addition, an operator may inadvertently actuate the machine by stepping, nudging or brushing against the front or side of the foot pedal switch causing unexpected operation as has occurred in the industrial setting on far too many occasions. Even if the foot pedal switch provided is completely enclosed and the danger zone or point of operation of the machine is properly guarded, it is foreseeable that injuries can and do occur. This is due to failure of or intentional by-passing of the machine guarding coupled with inadvertent machine actuation by the operator riding the pedal of the fully enclosed foot pedal switch.
Prior art attempts to solve problems relating to foot pedal devices include the device proposed by DiBonaventura in U.S. Pat. No. 3,759,115. DiBonaventura discloses a foot pedal switch having a guard covering the tops and sides of the switch. The foot pedal switch includes a mechanical stop which retains and locks the foot pedal switch in an unactuated position. The foot pedal switch requires the operator to use a specific insertion method for proper operation. While this approach eliminates many of the hazards posed by inadvertent machine operation caused by foreign objects, it does not prevent an operator from riding the pedal to achieve repetitive machine operation. In fact, the arrangement of the mechanical lock, requiring a fairly complex manipulation of the operator's foot, would tend to encourage the operator to develop a technique for riding the pedal so that it is unnecessary to go through the complex manipulation of the foot.
Another approach is disclosed in U.S. Pat. No. 3,916,722 to Grobe which discloses a foot pedal switch having a latch plate which is yieldably constrained to a restricting position after a latch mechanism is set. Again, the operator must go through a complex initial motion to move the shield and latch mechanism out of a restricting position. Furthermore, Grobe fails to disclose a means for preventing repetitive machine operation by riding the pedal.
U.S. Pat. No. 3,805,085 to Andrews discloses a complex relay circuit for use with palm button switches wherein an operator must actuate a first switch by passing his hands through a light beam prior to contacting the palm button switches. The breaking of the light beam initiates a first time interval within which the operator must strike two palm button switches before the machine will operate. The circuit disclosed in Andrews is a relay circuit which can be simply defeated by providing appropriate jumpers, thereby circumventing the safety features of the device. While the Andrews device discloses a single cycle limitation for operation of a machine, the complexity of the device and requirement that two light beams and palm buttons be contacted within a time interval unnecessarily complicates the operator's job and tends to encourage the operator to find a way to defeat the safety device. Andrews' invention requires the use of hand operated dual palm buttons coupled with light beam sensors. Thus, it is not appropriate for those requiring foot pedal switches. Furthermore, Andrews is not a self-contained single-actuation system which can be easily plugged or wired into an existing machine switch receptacle.
U.S. Pat. No. 5,166,513 to Keenan et al discloses a dual actuation foot switch for medical laser systems wherein the foot switch is enclosed in a housing having an opening for receiving a foot. Two switches. which may be contacted in the housing initiate two different responses from the medical laser system. The Keenan device does not disclose a fail-safe foot pedal switch wherein an operator is precluded from riding the pedal, but instead seems to suggest this is the preferred mode of operation for medical laser systems.
These and other disadvantages and problems inherent in the prior art are solved by the applicant's invention which is summarized below.